A PRESENTATION ON

“CENTRAL AND BOUNDARY VENTILATION”

PRANJAL SAO

TYPES OF VENTILATION SYSTEM

Depending on the relative position of intake and return airways, ventilation systems in mines can be broadly divided into the following

BOUNDARY OR UNIDIRECTIONAL CENTRAL OR BI DIRECTIONAL COMBINED

(a)Boundary ventilation system

The boundary ventilation system where the air flow unidirectional from the intake to the return through the working is by far the most efficient system necessitating the least use of ventilation control devices and thus resulting in a high volumetric efficiency of ventilation(70-80%).

It is commonly adopted in metal mines working steep lodes in the simplest form ,the intake and return shaft are located at the strike boundaries of the mine.

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This method is limited to mines having a small lateral extent only .sometimes at shallow levels of a developing mine having a relatively large lateral extent, small fans may be installed on top of winzes as shown in fig(1).

When air requirement varies widely from level to level ,each level may ventilated by an independent u/g fan as shown fig (3).

. With larger lateral extent, it is preferable

to have a central intake shaft with two return shaft or winzes at either boundary of the property fitted with two exhaust fan.(fig4)

Sometime a single forcing fan may be used on the top of intake shaft (fig5).

But this necessitates air lock on a hoisting shaft which is not very desirable.

. When the mine is extensive on the strick,it

may be divided into several lateral sections with separate fans as shown in fig(6).

Mines having workings in multiple parallel lodes are generally ventilated by separate exhaust fans installed on each lode ,though there may be a common intake.(fig7).

A less desirable alternative with a single forcing fan in shown in fig (8)

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Advantage of boundary ventilation system

1. the boundary ventilation system necessitates the minimum use of ventilation control devices. This apart form saving the capital invested on them as well as the cost of their operation and maintenance, reduces leakage and result in a high volumetric efficiency.

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2.different sections of the mine can be independently ventilated by separate fans. This reduces the total flow handled by a single fan and hence its head requirement .lower head results in less leakage . Airways of smaller cross-section can handle the flow . ventilation of each individual section can be independently controlled and a section can be isolated easily in the times of emergency.

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3. There is greater safety because of larger number of outlets to the surface.

4.Since developments have to be extended to the boundary right in the beginning in this system . the mine characteristic remains almost constant throughout the life of the mine thus resulting in a uniformly efficient operation of the fan. On the other hand ,the mine resistance goes on changing with the workings progressing towards

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The boundary of the property in the central system of ventilation where the fan has to negotiate a wider variation of mine characteristics.

Disadvantages of the boundary ventilation system

1. reversal of air flow is more complex. 2. separate fan installations increase the

cost of their operation ,supervision and maintenance.

Central or bidirectional ventilation system

The system is commonly adopted in in-the seam of coal mines where both intake and return shaft are located close by at the centre of the property . intake and return air from any district travel in opposite directions through parallel roadways usually separated by stopping erected in the cross-section between them . also return air from a district has to cross the intake in order to join the main return. Obviously the central ventilation system allows a substantial leakage because of the number of stopping and air crossing used so that volumetric efficiency is only 40-50% with this system .

Advantages of central ventilation system

1.the deposit can be worked after short development leading to a quicker start of production.

2.long development headings are not necessary and hence there is no associated problem of their ventilation.

3.central pits cause less loss of minerals in shaft pillers.

. 4. sinking of deep pits close together

economizes the cost of sinking as certain common facilities can be shared by the pit. On the other hand , boundary pit which are far off necessitate building of road, extension of power lines etc to the sinking site involving extra cost.

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5.both the central shafts can be used for hoisting ,but boundary shaft are rarely used for hoisting as this would required extension of surface transport to these pits. they how ever serve well as stowing pits (with hydraulic stowing pipes installed in them) if located on the rise side.